Radiation hardened MOS voltage generator circuit

Abstract

A voltage generator circuit for producing an output voltage which tracks the threshold voltage variation of the MOS devices on the semiconductor body, the magnitude of the output voltage being equal to or slightly greater than the absolute magnitude of the threshold voltages. The circuit includes two MOSFETs having their conduction paths connected in electrical series, each MOSFET having an applied gate-to-source voltage of 2V T . The voltage output terminal is connected to the node between the series connected conduction path terminals of the first and second MOSFETs. Three series connected MOSFETs which form a source follower circuit are also provided for providing the required gate-to-source voltage on the first two MOSFETs.

Having thus set forth a preferred embodiment of the invention, what is claimed is: 
     
       1. A voltage generator for tracking the threshold voltage variation of transistor devices comprising: a pair of terminals for connection across first and second sources of potential;   first and second transistor devices connected in electrical series between said first and said second source of potential; each of said transistor devices having respective conduction path terminals and a control terminal; a first node being formed at the common electrical junction between one of the conduction path terminals of said first transistor, and one of the conduction path terminals of said second transistor;   means for selectively applying a first potential to said control electrode of said first transistor device, comprising a field effect transistor source follower circuit, including: third and fourth enhancement mode field effect transistors, each having respective conduction path terminals and a control electrode, the conduction path terminals thereof being connected in electrical series between said first source of potential and said control terminal of said first enhancement mode transistor, a second node being formed at the common electrical junction between the conduction path terminals of said third transistor being connected to said second node and the control terminal of said fourth transistor being connected to the control terminal of said first transistor;   first control means connected to said control terminals of said first and fourth enhancement mode field effect transistors for selectively turning said transistors on;   a fifth enhancement mode field effect transistor having respective conduction path terminals and a control electrode, said conduction path terminals thereof being connected in electrical series with the conduction path of said third and fourth enhancement mode field effect transistor, the first conduction path terminal of said fifth transistor connected to the control terminal of said first transistor, the control terminal of said fifth transistor being connected to the control terminal of said second enhancement mode transistor;     means for selectively applying a second predetermined potential to said control electrode of said second transistor device; so that a voltage is generated on said first node substantially equal to the threshold voltage of said first and said second transistor devices; and   an output connected to said first node.   
     
     
       2. A voltage generator as defined in claim 1, wherein said first and second transistor devices are first and second enhancement mode MOS field effect transistors, each field effect transistor having source, gate, and drain electrodes. 
     
     
       3. A voltage generator as defined in claim 1, wherein said first and said second source of electrical potential are respectively a source of relatively positive and a source of relatively negative electrical potential. 
     
     
       4. A voltage generator as defined in claim 1, wherein said first source of potential is selectively controllable as a source of relatively positive potential or a source of relatively negative potential of predetermined magnitude, and said second source of potential is a source of relatively negative potential equal to said predetermined magnitude. 
     
     
       5. A voltage generator as defined in claim 1, wherein said means for selectively applying a first predetermined potential to said control electrode of said first transistor device applies a potential whose magnitude tracks said first source of potential such that the voltage between said first source of potential and said control electrode is equal to twice the threshold voltage. 
     
     
       6. A voltage generator as defined in claim 1, wherein the gate-to-source voltage of the first field effect transistor is equal to twice the threshold voltage, and the gate-to-source voltage of the second field effect transistor is equal to twice the threshold voltage. 
     
     
       7. A voltage generator as defined in claim 1 wherein said first and said second transistor devices are p-channel MOS field effect transistors, having source, gate, and drain electrodes, and said "worst case" bias level is a gate-to-source voltage of V DD . 
     
     
       8. A voltage generator as defined in claim 1, wherein said transistor devices are implemented in an integrated circuit on a sapphire substrate. 
     
     
       9. A voltage generator as defined in claim 1, wherein said first and said second transistor devices are n-channel MOS field effect transistors, having source, gate, and drain electrodes, and said "worst case" bias level is a gate-to-source voltage of V DD . 
     
     
       10. A voltage generator as defined in claim 1, wherein said third, fourth, and fifth transistor devices are n-channel MOS field effect transistors. 
     
     
       11. A voltage generator as defined in claim 1, for in said means for selectively applying a second predetermined potential comprises a complementary MOS field effect transistor circuit. 
     
     
       12. A voltage generator as defined in claim 11, wherein said complementary MOS field effect transistor circuit comprises a first P channel MOS field effect transistor connected in electrical series with a second N channel field effect transistor; a third node being formed at the common electrical junction between one of the conduction path terminals of said first complementary MOS transistor and one of the second conduction path terminals of the second complementary MOS transistor, said third node being connected to said control electrode of said second control transistor device. 
     
     
       13. A voltage generator as defined in claim 12, further comprising activating means connected to the control electrodes of said first and second complementary transistor devices for turning said first complementary MOS transistor devices off and said second MOS transistor device on so that a conduction path is provided between said third, fourth, fifth enhancement mode field effect transistor, said second complementary MOS transistor, and ground. 
     
     
       14. An integrated voltage generator circuit for tracking the threshold voltage variation of transistor devices comprising; a pair of terminals for connection across first and second sources of electrical potential;   first and second transistor devices connected in electrical series between said first and said second terminals; each of said transistor devices having respective conduction path terminals and a control terminals; a first node being formed at the common electrical junction between one of the conduction path terminals of said first transistor, and one of the conduction path terminals of said second transistor;   means for selectively applying a first potential to said control electrode of said first transistor device;   means for selectively applying a second potential to said control electrode of said second transistor device; so that a voltage is generated on said first node substantially equal to the threshold voltage of said first and said second transistor devices; and   an output connected to said first node, characterized in that said means for applying second potential comprises two complementary MOS defined effect transistors.   
     
     
       15. A voltage generator as defined in claim 14, characterized in that said first and second transistor devices are first and second enhancement mode MOS field effect transistors, each field effect transistor having source, gate, and drain electrodes. 
     
     
       16. A voltage generator as defined in claim 15, characterized in that said first and said second source of electrical potential are a source of relatively positive and a source of relatively negative electrical potential respectively. 
     
     
       17. A voltage generator as defined in claim 14, characterized in that said first source of potential is selectively controllable as a source of relatively positive potential or a source of relatively negative potential of predetermined magnitude, and said second source of potential is a source of relatively negative potential equal to said predetermined magnitude. 
     
     
       18. A voltage generator as defined in claim 14, characterized in that said means for selectively applying a first predetermined potential to said control electrode of said first transistor device applies a potential whose magnitude tracks said first source of potential are such that the voltage between said first source of potential and said control electrode is equal to twice the threshold voltage. 
     
     
       19. A voltage generator for tracking the threshold voltage variation of transistor devices comprising: a variable first and substantially fixed second source of electrical potential;   first and second transistor devices connected in electrical series between said first and said second source of potential; a third transistor device connected in electrical series between said first transistor device and said second source of potential and in parallel with said second transistor device, each of said transistor devices having respective conduction path terminals and a control terminal; a first node being formed at the common electrical junction between one of the conduction path terminals of said first transistor, and one of the conduction path terminals of said second transistor;   means for selectively applying a first predetermined potential to said control electrode of said first transistor device;   means for selectively applying a second predetermined potential to said control electrode of said second transistor device; so that a voltage is generated on said first node substantially equal to the threshold voltage of said first and said second transistor devices; and   an output connected to said first node.   
     
     
       20. A voltage generator as defined in claim 19 wherein said variable first source of electrical potential includes a normal mode at a relatively positive potential and a standby mode at a relatively negative potential. 
     
     
       21. A voltage generator as defined in claim 16, characterized in that the gate-to-source voltage of the first field effect transistor is equal to twice the threshold voltage, and the gate-to-source voltage of the second field effect transistor is equal to twice the threshold voltage. 
     
     
       22. A voltage generator as defined in claim 16, characterized in that said means for applying a first predetermined potential comprises a field effect transistor source follower circuit. 
     
     
       23. A voltage generator as defined in claim 22, characterized in that said source follower circuit comprises: third and fourth enhancement mode field effect transistors each having respective conduction path terminals and a control electrode, the conductor path terminals thereof being connected in electrical series between said first source of potential and said control terminal of said first enhancement mode transistor, a second node being formed at the common electrical junction between the conduction path terminals of said third and fourth transistors, the control terminal of said third transistor being connected to said second node and the control terminal of said fourth transistor being connected to the control terminal of said first transistor.   
     
     
       24. A voltage generator as defined in claim 23, characterized in that said source follower circuit further comprises a fifth enhancement mode field effect transistor having respective conduction path terminals and a control electrode, said conduction path terminals thereof being connected in electrical series with the conduction path of said third and fourth enhancement mode field effect transistor, the control terminal of said fifth transistor being connected to the control terminal of said fifth transistor being connected to the control terminal of said second enhancement mode transistor. 
     
     
       25. A voltage generator as defined in claim 23, characterized in that the generator further comprises control input means connected to said control terminals of said third and fourth enhancement mode field effect transistors for selectively turning said transistors on. 
     
     
       26. A voltage generator as defined in claim 23, characterized in that the generator further comprises first control means connected to said third and fourth enhancement mode field effect transistors for selectively turning such transistors off and applying a predetermined potential to the control electrodes of said first and second transistors. 
     
     
       27. A voltage generator as defined in claim 26, characterized in that the generator further comprises second control means for providing a control signal to said second node. 
     
     
       28. A voltage generator as defined in claim 26, characterized in that said means for applying a first predetermined potential and said means for applying a second predetermined potential to selectively bias said first and said second transistor devices respectively at the "worst case" bias level in terms of the relative change in the threshold voltage before and after irradiation, a voltage equal to said second source of potential being developed at said output. 
     
     
       29. A voltage generator as defined in claim 26 characterized in that said first and said second transistor devices are p-channel MOS field effect transistors, having source, gate, and drain electrodes, and said "worst case" bias level is a gate-to-source voltage of V DD , with the drain and source at V SS  and the gate at V DD . 
     
     
       30. A voltage generator as defined in claim 26 characterized in that said first and said second transistor devices are n-channel MOS field effect transistors. 
     
     
       31. A voltage generator as defined in claim 26 wherein said third, fourth, and fifth transistor devices are n-channel MOS field effect transistors. 
     
     
       32. A voltage generator as defined in claim 19, wherein said first and said third transistor devices are complementary MOS transistors of opposite conductivity. 
     
     
       33. A voltage generator as defined in claim 19, wherein said first and second transistor devices are first and second enhancement mode MOS field effect transistors, each field effect transistor having source, gate, and drain electrodes. 
     
     
       34. A voltage generator as defined in claim 19, wherein said first and said second source of electrically potential are respectively a source of relatively positive and a source of relatively negative electrical potential. 
     
     
       35. A voltage generator as defined in claim 19, wherein said first source of potential is selectively controllable as a source of relatively positive potential or a source of relatively negative potential of predetermined magnitude, and said second source of potential is a source of relatively negative potential equal to said predetermined magnitude. 
     
     
       36. A voltage generator as defined in claim 19, wherein said means for selectively applying a first predetermined potential to said control electrode of said first transistor device applies a potential whose magnitude tracks said first source of potential such that the voltage between said first source of potential and said control electrode is equal to twice the threshold voltage. 
     
     
       37. A voltage generator as defined in claim 33, wherein the gate-to-source voltage of the first field effect transistor is equal to twice the threshold voltage, and the gate-to-source voltage of the second field effect transistor is equal to twice the threshold voltage.